1. Field of the Invention
This invention relates to copolymers of long-chain alkyl acrylates with N-containing olefins, the process for their production and their use as flow improvers for crude oils.
2. Description of the Related Art
Depending on their respective origin, crude oils can contain considerable amounts of paraffins. When cooled below a certain temperature (cloud point) the paraffin gradually crystallizes out of the oil and forms a three-dimensional network of scales and/or needles which is filled with oil. Such a structure gives the crude oil disadvantageous properties with respect to flowability and ease of handling.
The effect of the paraffin crystallizing out in the crude oil is that the oil scarcely or no longer flows, it can no longer be pumped or only with a great expenditure of energy and forms deposits in the pipelines, storage containers and ships tanks, which lead to considerable losses in production and capacity.
Crude oils found in oil-bearing layers have a temperature which varies according to depth. In the deeper layers from which the oil is extracted, higher temperatures prevail at which the paraffin is still fluid and dissolved in the oil. If crystallisation inhibitors are added to a crude oil containing paraffin in this state, the effect is on the one hand to lower the solidification point, and on the other hand to alter the crystal structure of the separated paraffin with improvement of the flow properties of the crude oil.
As a measure of the effect of a flow improver the solidification point or the lowering of the solidification point in comparison to the crude oil without flow improvers is given in .degree.C. It is in this sense possible to speak of pour-point depressants, PPDs, as well as flow improvers.
In the prior art a number of compounds with a crystallisation inhibiting effect are described, see DE-OS 2,926,474, 3,237,308, 3,226,252, 2,210,431; EP-OS 61, 894; U.S. Pat. Nos. 4,663,491, 4,284,414, 3,957,659, 3,854,893. Usually these are co-polymers of C.sub.16 C.sub.24 methacrylates with short chain methacrylates, aminoalkylmethacrylates as well as various olefins with or without polar groups. The C.sub.16 C.sub.24 -alcohols characteristically represent the usual cuts of the product from untreated or petrochemical raw materials.
A special position is held by a commercial product, which is used for comparison purposes in the following and is therefore described as a "comparative product" and can be used in many different crude oils as a flow improver. The exact structure of this product is not known, presumably it is one of the co-polymers described in U.S. Pat. Nos. 3,957,659 and 3,868,231 of
(a) a C.sub.16 C.sub.24 -acrylate and (b) 4-vinylpyridine.
The two comonomers have very different copolymerization parameters (acrylic acid octyl ester:v.sub.1 approximately 0.1: 4-vinylpyridine:v.sub.2 approximately 1.6). They are therefore difficult to co-polymerize and require special measures (e.g. a programmed "Monomer Addition Procedure") in the products.